1. Field of the Invention
The present invention relates to a ceramic composite multilayer substrate, a method for manufacturing the same, and electronic components.
2. Description of the Related Art
As techniques relating to ceramic multilayer substrates, the techniques described in Japanese Unexamined Patent Application Publication No. 05-136572, Japanese Unexamined Patent Application Publication No. 2005-210036 and Japanese Unexamined Patent Application Publication No. 2005-223226 are known, for example. Japanese Unexamined Patent Application Publication No. 05-136572 describes a method for manufacturing a multilayer ceramic substrate, and Japanese Unexamined Patent Application Publication No. 2005-210036 and Japanese Unexamined Patent Application Publication No. 2005-223226 each describes a composite multilayer substrate.
The method for manufacturing a multilayer ceramic substrate described in Japanese Unexamined Patent Application Publication No. 05-136572 includes producing a green sheet at least containing an organic binder and a plasticizer in a glass ceramic low-temperature sintered substrate material, forming an electrode pattern with a conductive paste composition, and laminating the raw sheet and a required number of other green sheets on which an electrode pattern have been formed. After an appropriate period of time, a green sheet containing an inorganic composition that is not sintered at the firing temperature of the glass/ceramic low-temperature sintered substrate material is laminated on both sides or either side of the green sheet laminate containing low-temperature sintered glass/ceramics so as to be interposed, and firing the laminate. After an appropriate period of time, the inorganic composition that is not sintered is charged with a resin to form a top layer wiring.
A composite multilayer substrate described in Japanese Unexamined Patent Application Publication No. 2005-210036 has a ceramic substrate and a resin layer, in which the ceramic substrate has a circuit pattern, the resin layer has an external terminal electrode on the undersurface, the undersurface of the ceramic substrate and the upper surface of the resin layer are joined to each other, the circuit pattern and the external terminal electrode are electrically connected to each other, and the thermal expansion coefficient of the ceramic substrate is in the range of 10.0 ppm/° C. to 20.0 ppm/° C. at 20° C. to 300° C. Since the composite multilayer substrate has such a structure, layer separation between the ceramic substrate and the resin layer can be prevented.
A composite multilayer substrate described in Japanese Unexamined Patent Application Publication No. 2005-223226 is a composite multilayer substrate having a ceramic multilayer substrate and a resin laminate in which a first resin layer, a second resin layer, and a third resin layer are laminated, in which the undersurface of the ceramic multilayer substrate and the upper surface of the resin laminate are joined to each other and the first, second, and third resin layers each have a different thermal expansion coefficient. In this composite multilayer substrate, a gradient structure is given to the thermal expansion coefficient because there is a possibility that layer separation or cracks may occur due to thermal shock at an interface having a large thermal expansion coefficient difference when the thermal expansion coefficient of a composite resin material layer is adjusted to the thermal expansion coefficient of either one of the ceramic substrate or a printed-circuit board.
According to the method described in Japanese Unexamined Patent Application Publication No. 05-136572 including sandwiching a laminate containing a ceramic green sheet for a base material layer containing a glass/ceramic low-temperature sintered compact substrate material and having a given electrode pattern with a ceramic green sheet for a constraining layer containing an inorganic composition that is not sintered at the firing temperature of the glass/ceramic low-temperature sintered compact substrate material and having a given electrode pattern, firing the same, charging a resin into the non-sintering inorganic composition, and, after an appropriate period of time, forming the top surface wiring has the following problems. The multilayer ceramic substrate itself tends to undergo firing shrinkage. Therefore, the porosity particularly near the interface of the multilayer ceramic substrate of the non-sintering inorganic composition layer becomes small. Therefore, the resin cannot be sufficiently charged into the portion, and the pores sometimes remain. Moreover, the resin charged state is likely to vary, and the reliability of the obtained substrate sometimes decreases.
According to the techniques of Japanese Unexamined Patent Application Publication No. 2005-210036 and Japanese Unexamined Patent Application Publication No. 2005-223226, even when the thermal expansion coefficient difference between the printed-circuit board and the ceramic substrate is large when the composite multilayer substrate is mounted on the printed-circuit board, the generation of cracks due to the thermal expansion coefficient difference between the printed-circuit board and the ceramic substrate can be prevented by the resin layer or the resin laminate. However, when the ceramic substrate is warped before the formation of the resin layer or the ceramic substrate is warped due to the formation of the resin layer, cracks are likely to occur. In recent years, a reduction in the height of ceramic electronic devices has been strongly demanded and a further reduction in the thickness of the ceramic substrate has been demanded. Due to the reduction in the layer thickness, the ceramic substrate is likely to be warped or cracks are likely to occur during resin curing. In such a case, the generation of cracks is difficult to suppress.
In particular, the technique of Japanese Unexamined Patent Application Publication No. 2005-223226 is required to form at least two resin layers and to form a conductor wiring portion for every resin layer, for example. Thus, the technique of Japanese Unexamined Patent Application Publication No. 2005-223226 requires a greater number of processes other than the process of forming two or more resin layers. Furthermore, since the resin layer is formed more than once, position shift or the like occurs between the resin layers while laminating the resin layers, reducing the lamination accuracy so as to deteriorate the shape of the resin layers deteriorates, and thus the composite multilayer substrate is likely to deform.
In addition to the reduction in the height, the composite multilayer substrate is required to reduce irregularities (small wave-like distortions) on the ceramic substrate. According to the method including forming the resin layer more than once, it has been difficult to make the thickness of the ceramic substrate uniform after the formation of the substrate is completed and moreover it has been difficult to smooth the resin layer on the substrate surface. Moreover, when the resin layer is formed more than once, it has been required to form a wiring structure whenever forming each resin layer. Accordingly, the same process is repeatedly performed when forming the resin layer, which has caused problems in that the manufacturing method has become complicated and structural defects have been likely to occur when forming a wiring structure.